FIG. 25 is a block diagram showing a conventional image comparison system. This conventional image comparison system comprises an image input means 115, image converting means 117, image comparing means 157, reference image storing unit 130, and standard three-dimensional object model storing unit 135.
Reference images obtained by sensing the images of objects are prestored in the reference image storing unit 130. Standard three-dimensional object models are prestored in the standard three-dimensional object model storing unit 135. The image converting means 117 generates a partial image by converting one or both of an input image from the image input means 115 and each reference image obtained from the reference image storing unit 130 such that the pose conditions are the same, in relation to a partial image common to the input image and reference image, by using a three-dimensional object model obtained from the standard three-dimensional object model storing unit 135.
A partial region is a characteristic portion such as an eye, nose, or mouth. Partial regions can be related to each other by designating feature points in images and three-dimensional object models beforehand. The image comparing means 157 compares the partial images of the input image and each reference image converted by the image converting means 117, calculates average similarity degrees, and selects a reference image having the largest similarity degree for each object (e.g., Japanese Patent Laid-Open No. 2000-322577 (patent reference 1)).
FIG. 26 is a block diagram showing another conventional image comparison system. This conventional image comparison system comprises an image input means 115, illumination change correcting means 122, image converting means 118, image comparing means 158, reference image storing unit 130, and standard three-dimensional object model storing unit 135.
Reference images obtained by sending the images of objects are prestored in the reference image storing unit 130. Standard three-dimensional object models are prestored in the standard three-dimensional object model storing unit 135. The illumination change correcting means 122 estimates the illumination condition (surface reflectance) of an input image from the image input means 115, by using a three-dimensional object model obtained from the standard three-dimensional object model storing unit 135. The image converting means 118 generates an image by converting the input image by using a three-dimensional object model so as to meet the illumination condition of a reference image. The image comparing means 158 compares the input image converted by the image converting means 118 with individual reference images, calculates similarity degrees, and selects a reference image having the largest similarity degree for each object (e.g., Japanese Patent Laid-Open No. 2002-024830 (patent reference 2)).
FIG. 27 is a block diagram showing still another conventional image comparison system. This conventional image comparison system comprises an image input means 115, reference three-dimensional object model storing unit 137, and pose estimating/comparing means 150. The pose estimating/comparing means 150 includes a pose candidate deciding means 120, comparison image generating means 140, and image comparing means 155.
Reference three-dimensional object models generated by measuring objects are prestored in the reference three-dimensional object model storing unit 137. The pose estimating/comparing means 150 calculates a minimum distance value (or a maximum similarity degree) between an input image obtained from the image input means 115 and each reference three-dimensional object model obtained from the reference three-dimensional object model storing unit 137, and selects a model having the smallest minimum distance value.
More specifically, the pose candidate deciding means 120 generates at least one pose candidate. Then, the comparison image generating means 140 generates a comparison image close to an input image while projecting a reference three-dimensional object model onto a two-dimensional image in accordance with the pose candidate. The image comparing means 155 calculates a distance value between the comparison image and the input image, and selects a comparison image having the smallest distance value for each model, thereby estimating an optimum pose and obtaining a minimum distance value between the input image and the reference three-dimensional object model. In addition, the image comparing means 155 selects a model having the smallest minimum distance value (e.g., Japanese Patent Laid-Open No. 2003-058896 (patent reference 3)).